There are 3 basic mechanisms that can cause interruption of cerebral blood flow: embolism from the endocardium blocking downstream arterial flow; local occlusion: often due to proximal or distal in situ thrombosis; and whole brain hypoperfusion. Most ischemic strokes are due to embolism (25% cardiogenic embolism) and in situ thrombosis, and a few are due to chronic hypoperfusion. In macrovascular disease, all 3 of these mechanisms may be involved. For example, severe stenosis of one carotid artery (caused by a large atherosclerotic plaque), distal ischemia due to emboli and/or further stenosis and distal hypoperfusion from acute plaque rupture and thrombosis, and cerebral hypoperfusion can be further exacerbated by both low cardiac output and extracorporeal hypocirculation. At a certain stage of cerebrovascular disease, a certain mechanism of occurrence may play a primary role and other mechanisms may play a secondary role. 1, embolism: a, arterial-arterial embolism (1) intracranial and extracranial macrovascular lesions of any cause atherosclerosis is the most common; non-atherosclerotic disease (myofibrillar dysplasia, entrapment, vascular tortuosity, vasculitis/arteritis, vasospasm, vasoconstriction, etc.) (2) aortic arch abnormalities of any cause (atherosclerosis, entrapment/aneurysm, connective tissue disease, infection, etc.) b , cardiogenic embolism (1) arrhythmias (atrial fibrillation is common); (2) heart valve disease. rheumatic heart disease, prosthetic heart valve disease, endocarditis (infectious, non-bacterial embolic). 2, local occlusion; a, small vessel lesions from any cause; (1) multiple cause related (hypertension, diabetes, hyperlipidemia, smoking, alcohol, etc.); (2) cerebral arteritis; (3) cerebral amyloid angiopathy. b, coagulation abnormalities; malignant disease; hormonal: pregnancy and puerperium, oral contraceptives, hormone replacement, etc.; hereditary coagulopathy; c, abnormal platelet function heparin-induced thrombocytopenia thrombocytopenic purple; d, hyperviscosity hyperfibrinemia sickle cell anemia erythrocytosis. 3, hypoperfusion a, extracorporeal hypocirculation from any cause; b, heart failure/low cardiac output; c, cardiac arrest, arrhythmias.